Optical information-recording medium, novel oxonol compound and method of recording information

ABSTRACT

An optical information-recording medium which contains a dye having at least two chromophores bonded to each other without any conjugated bond intervening between those chromophores.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat-mode information recordingmedium and an information recording method which enable write (record)and read (playback) of information by use of high energy density laserlight. More specifically, the invention relates to a heat-modeinformation recording medium, such as a recordable digital versatiledisc (DVD-R), which is suitable for recording information by use ofvisible laser light.

2. Description of the Related Art

Information recording media on which information is recordable only onceby use of laser light (optical discs) have been long known. Theinformation recording media of such a type are referred to as recordableCDs (the so-called CD-R) as well. These disc shave an advantage in thatthey can be rapidly delivered in low quantities at reasonable prices,compared with traditional CDs, and the demand for them has been growingas personal computers have come into widespread use recently. A typicalstructure of CD-R type of information recording media is a laminate inwhich a transparent disk-shape substrate, a recording layer containingorganic dyes, a reflective layer made of metal such as gold and aprotective layer made of resin are arranged in the order of mention.

And such optical discs can have information recorded thereon by beingirradiated with laser light in the near infrared region (generally laserlight of wavelengths in the vicinity of 780 nm) and undergoing localheat generation and deformation in their respective recording layers. Onthe other hand, reading (playback) of information from discs isgenerally performed by irradiating the discs with laser light of thesame wavelength as the laser light used for recording has, and detectingdifferences in reflectivities between the areas deformed by heatgeneration (recorded area) and the areas remaining undeformed(unrecorded area) in the recording layers.

In recent years information recording media have been required to havehigher recording densities. In order to heighten the recordingdensities, it is known to be effective that the diameter of laser lightused for irradiation is narrowed down. Moreover, irradiation with laserlight of shorter wavelengths is known to be theoretically moreadvantageous to further increase in recording density, because thediameter of laser light can be made more narrow the shorter the laserlight is in wavelength. Therefore, the development of optical discssuitable for record and playback with laser light of wavelengths shorterthan hitherto used 780 nm has been pursued. For instance, optical discsreferred to as recordable digital video discs (the so-called DVD-R) havebeen offered. These optical discs are each manufactured so as to have astructure that two disks which each have on a 120-mm-dia or 80-mm-diatransparent disk-shape substrate, wherein is formed a pregroove having a0.8-μm track pitch smaller than 1.6 μm adopted as the track pitch ofCD-R, a dye-containing recording layer, a reflective layer and aprotective layer in the order of mention are bonded together with therecording layers inside, or one disk as described above and a disk-shapeprotective substrate having almost the same dimensions are bondedtogether with the recording layer inside. And the record and theplayback of DVD-R are performed by irradiation with visible laser light(generally in the wavelength range of 600 to 700 nm). Therefore, DVD-Ris considered to enable high-density recording, compared with CD-R typeof optical discs.

As the information recording medium of DVD-R type can record informationseveral times as much as that of a hitherto used information recordingmedium of CD-R type, it is desired that the information recording mediumof DVD-R type has not only high recording sensitivity but also a lowincidence of errors even in high-speed recording made out of necessityto process rapidly high-volume information in particular. In addition,it is desired to develop a recording layer capable of retaining itsproperties with stability for a long time even under exposure to lightor heat, because a dye-containing recording layer is generally not sostable to prolonged exposure to heat or light.

JP-A-10-226170 discloses the DVD-R type of information recording mediumhaving on a substrate a recording layer containing a certain cyaninedye. Therein, it is stated that the cyanine dye compound as specifiedcan ensure high recording sensitivity and high reflectivity in theinformation recording medium. Further, JP-A-2001-287456 discloses theinformation recording medium having on a substrate a recording layercontaining a cyanine dye of a specific structure, and states that such acyanine dye enables the recording medium to have excellent recordingcharacteristics and retain its recording characteristics with stabilityfor a long time. On the other hand, JP-A-63-209995 discloses the CD-Rtype of information recording medium having an oxonol dye-containingrecording layer provided on a substrate, and states that the use of sucha dye compound enables long-term retention of steady record and playbackcharacteristics. Therein, the oxonol dye compounds having ammonium ionsintroduced therein for forming salts are disclosed. In addition,JP-A-2000-52658 discloses the oxonol dye compounds providing opticalinformation-recording media with high light resistance and durability aswell as excellent recording characteristics.

SUMMARY OF THE INVENTION

The present Inventors used various cyanine dye compounds and oxonol dyecompounds as disclosed in the documents cited above in opticalinformation-recording media of DVD-R type and studied performancecapabilities of the resulting recording media. As a result, it has beenfound that while the DVD-R type of optical information-recording mediacontaining those dye compounds in their respective recording layersshowed very excellent recording characteristics in the low-speedrecording at equivalent or double speed, they fell short of deliveringpractically sufficient performances in respects of modulation factor andreflectivity although they can show comparatively excellent recordingcharacteristics at the time of high-speed recording at quadruple orhigher speed. The use of a dye having an optical characteristic that thecomplex refractive index (n+ik) of the dye is greater in the real part nthan those of dyes for low-speed recording use and its imaginary part kis almost the same as or smaller than those of dyes for low-speedrecording use can serve the purpose of obtaining an opticalinformation-recording medium which can maintain satisfactory recordingcharacteristics in the recording at a low speed such as an equivalent ordouble speed and, at the same time, can satisfy recording performances,including sufficient reflectivity and modulation factor in particular,even in the recording at a high speed such as a quadruple or higherspeed. However, it was very difficult to obtain dyes showing complexrefractive indexes great in real part n and almost equal or small inimaginary part k, compared with those of dyes for low-speed recordinguse, while maintaining satisfactory low-speed recording characteristics.Therefore, an object of the invention is to provide a dye having acomplex refractive index great in real part n and almost equal or smallin imaginary part k, compared with those of dyes for low-speed recordinguse, and thereby ensuring a high reflectivity and a high modulationfactor even in high-speed recording at quadruple or higher speed as itmaintains satisfactory recording characteristics in low-speed recordingat equivalent to double speed. Another object of the invention is toprovide a dye attaining sufficiently low jitter at a wide range ofrecording speeds covering from equivalent- to octuple-speed recording.

As a result of our intensive studies, it has been found that the desiredoptical characteristics as mentioned above can be achieved by impartingthe following specific molecular structures to dyes.

The following are embodiments of the invention:

(1) An optical information-recording medium, comprising a dye having atleast two chromophores that are bonded to each other without anyconjugated bond intervening between the chromophores (preferably in arecording layer). The optical information-recording medium is preferablya heat-mode optical information-recording medium having on a substrate arecording layer capable of recording information by irradiation withlaser light.

(2) A heat-mode optical information-recording medium as described in(1), having a thickness of 1.2±0.2 mm and comprising two laminates eachcontaining a recording layer including the dye, in which the twolaminates are bonded each other so that each of the recording layers isinside, wherein each of the laminates includes a transparent disk-shapesubstrate having a pregroove formed with a track pitch of 0.6 to 0.9 μmand measuring one of 120±3 mm and 80±3 mm in diameter and 0.6±0.1 mm inthickness; and the recording layer provided on the pregroove-formed sideof the transparent disk-shape substrate; or a heat-mode opticalinformation-recording medium as described in (1), having a thickness of1.2±0.2 mm, the optical information-recording medium comprising alaminate containing a recording layer including the dye and a disk-shapeprotective plate, in which the laminate and the disk-shape protectiveplate are bonded each other so that the recording layer is inside,wherein the laminate includes a transparent disk-shape substrate havinga pregroove formed with a track pitch of 0.6 to 0.9 μm and measuring oneof 120±3 mm and 80±3 mm in diameter and 0.6±0.1 mm in thickness; and therecording layer provided on the pregroove-formed side of the transparentdisk-shape substrate.

(3) An optical information-recording medium as described in (1) or (2),wherein the dye is represented by the following formula (1):

wherein Dye¹¹, Dye¹² and Dye^(2K) each independently represents a dyeresidue having a chromophore, L¹¹ and L^(2k) each independentlyrepresent a divalent linkage group forming π-conjugated system betweenchromophores linked thereby, n represents an integer of 0 to 10, krepresents every integer in the 0 to n range, Q represents an ionneutralizing electric charge, and y is a number required forneutralization of electric charge.

(4) An optical information-recording medium as described in (3), whereinthe chromophore forming the dye residue represented by any of Dye¹¹,Dye¹² and Dye^(2k) is at least one of cyanine dyes, merocyanine dyes andoxonol dyes.

(5) An optical information-recording medium as described in (3) or (4),wherein all the chromophores forming the dye residues represented byDye¹¹, Dye¹² and Dye^(2k) are oxonol dyes.

(6) An optical information-recording medium as described in any of (1)to (5), wherein the dye is of a structure represented by the followingformula (6):

wherein Za²¹, Za²², Za²³ and Za²⁴ each independently represents atomsforming an acidic nucleus, Ma²¹, Ma²², Ma²³, Ma²⁴, Ma²⁵ and Ma²⁶ eachrepresent a substituted or unsubstituted methine group independently,L¹¹ is a divalent linkage group forming no π-conjugated system togetherwith its two bonds, Ka²¹ and Ka²² each represent an integer of 0 to 3independently, and Q represents a univalent cation for neutralizingelectric charge or 2Q represents a divalent cation; and Ma²¹s, Ma²²s,Ma²⁵s and Ma²⁶s present when Ka²¹ and Ka²² are each 2 or 3 may be thesame or different.

(7) An oxonol compound represented by the following formula (2):

wherein R¹¹, R¹², R¹³ and R¹⁴ each independently represents a hydrogenatom, a substituted or unsubstituted alkyl group, a substituted orunsubstituted aryl group or a substituted or unsubstituted heterocyclicgroup, R²¹, R²² and R³ each independently represents a hydrogen atom, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedalkoxy group, a substituted or unsubstituted aryl group, a substitutedor unsubstituted aryloxy group, a substituted or unsubstitutedheterocyclic group, a halogen atom, a carboxyl group, a substituted orunsubstituted alkoxycarbonyl group, a cyano group, a substituted orunsubstituted acyl group, a substituted or unsubstituted carbamoylgroup, an amino group, a substituted amino group, a sulfo group, ahydroxyl group, a nitro group, a substituted or unsubstitutedalkylsulfonylamino group, a substituted or unsubstitutedarylsulfonylamino group, a substituted or unsubstituted carbamoylaminogroup, a substituted or unsubstituted alkylsulfonyl group, a substitutedor unsubstituted arylsulfonyl group, a substituted or unsubstitutedalkylsulfinyl group, a substituted or unsubstituted arylsulfinyl groupor a substituted or unsubstituted sulfamoyl group, m represents aninteger of 0 or more, R³s may be the same or different when m is 2 ormore, Z^(X+) represents a cation, and x represents an integer of 1 ormore.

(8) An optical information-recording medium as described in any of (1)to (6), wherein the dye is an oxonol compound represented by formula (2)defined in (7).

(9) A method of recording information comprising recording informationon an optical information-recording medium as described in any of (1) to(6) and (8) by irradiation with laser light having a wavelength of 600to 700 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing recording strategies used in Example andComparative Examples.

DETAILED DESCRIPTION OF THE INVENTION

The invention is illustrated below in detail. Additionally, when aspecific moiety is referred to as “a group” in the invention, the term“group” means that the moiety may have at least one (to the greatestpossible number) substituent or no substituent unless otherwiseindicated. For instance, the term “an alkyl group” is intended toinclude substituted and unsubstituted alkyl groups. Moreover, thesubstituents usable in the present compounds may include anysubstituents whether they further have substituents or not. And when aspecific moiety is referred to as “a ring” or “a group” contains “aring” in the invention, the “ring” may be a single ring or a condensedring, or it may be substituted or unsubstituted, unless otherwiseindicated. For instance, “an aryl group” may be a phenyl group, or anaphthyl group, or a substituted phenyl group.

In formula (1), Dye¹¹, Dye¹² and Dye^(2k) each represent a dye residuehaving a chromophores independently. The chromophore forming the dyeresidue represented by Dye¹¹, Dye¹² and Dye^(2k) each has no particularrestrictions. Included among its examples are cyanine dyes, styryl dyes,merocyanine dyes, phthalocyanine dyes, oxonol dyes, azo dyes, azamethinedyes, squarylium dyes and metal chelate compolex dyes. Suitable examplesof chromophores forming dye residues forming Dye¹¹, Dye¹² and Dye^(2k)include cyanine dyes, merocyanine dyes, oxonol dyes, phthalocyaninedyes, or metal chelate dyes. Of these dyes, cyanine dyes, merocyaninedyes or oxonol dyes, especially cyanine dyes or oxonol dyes, arepreferred over the others as the chromophores forming dye residuesrepresented by Dye¹¹, Dye¹² and Dye^(2k). The chromophores forming dyeresidues represented by Dye¹¹, Dye¹² and Dye^(2k) may be different fromone another, but it is preferable that they are the same.

When the chromophores forming dye residues represented by Dye¹¹, Dye¹²and Dye^(2k) are cyanine dyes, the cyanine dyes are preferably thoserepresented by the following formula (3):

In the above formula, Za¹ and Za² each represent atoms forming a 5- or6-membered nitrogen-containing heterocyclic ring which may further befused together with a benzene ring, a benzofuran ring, a pyridine ring,a pyrrole ring, an indole ring or a thiophene ring.

Ra¹ and Ra² each represent any of a hydrogen atom, a substituted orunsubstituted alkyl group (preferably containing 1 to 20 carbon atoms,with examples including methyl, ethyl, n-propyl, isopropyl, n-butyl,n-pentyl, benzyl, 3-sulfopropyl, 4-sulfopropyl, 3-methyl-3-sulfopropyl,2′-sulfobenzyl, carboxymethyl and 5-carboxypentyl groups), a substitutedor unsubstituted alkenyl group (preferably containing 2 to 20 carbonatoms, with examples including vinyl and allyl groups), a substituted orunsubstituted aryl group (preferably containing 6 to 20 carbon atoms,with examples including phenyl, 2-chlorophenyl, 4-methoxyphenyl,3-methylphenyl and 1-naphthyl groups) and a substituted or unsubstitutedheterocyclic group (preferably containing 1 to 20 carbon atoms, withexamples including pyridyl, thienyl, furyl, thiazolyl, imidazolyl,pyrazolyl, pyrrolidino and morpholino groups), preferably any of ahydrogen atom, a substituted or unsubstituted alkyl group and asubstituted or unsubstituted sulfoalkyl group, far preferably either ofa substituted or unsubstituted alkyl group or a substituted orunsubstituted sulfoalkyl group.

Ma¹ to Ma⁷ each represent a methine group independently. The methinegroup may have a substituent. Suitable examples of such a substituentinclude a 1-20C alkyl group (e.g., methyl, ethyl, i-propyl), a halogenatom (e.g., chlorine, bromine, iodine, fluorine), a nitro group, a 1-20Calkoxy group (e.g., methoxy, ethoxy), a 6-26C aryl group (e.g., phenyl,2-naphthyl), a 0-20C heterocyclic group (e.g., 2-pyridyl, 3-pyridyl), a6-20 caryloxy group (e.g., phenoxy, 1-naphthoxy, 2-naphthoxy), a 1-20Cacylamino group (e.g., acetylamino, benzoylamino), a 1-20C carbamoylgroup (e.g., N,N-dimethylcarbamoyl), a sulfo group, a hydroxyl group, acarboxyl group, a 1-20C alkylthio group (e.g., methylthio) and a cyanogroup. In addition, the methine group may form a ring together withanother methine group, or it can form a ring in combination with anauxochrome.

It is preferable that Ma¹ to Ma⁷ are each an unsubstituted methinegroup, an ethyl-substituted methine group or a methyl-substitutedmethine group independently.

na¹ and na² each represent 0 or 1 independently, and it is preferablethat they are each 0. ka¹ represents an integer of 0 to 3, preferably aninteger of 0 to 2, far preferably 1 or 2. When ka¹ is 2 or 3, Ma³s andMa⁴s may be the same or different. Q represents an ion neutralizingelectric charge, and y is a number required for neutralization ofelectric charge.

Incidentally, the dye residue formed by removing a hydrogen atom fromany of Za¹, Za², Ra¹, Ra² and Ma¹ to Ma⁷ in formula (3) can be chosen asa dye residue in formula (1) and enter into combination with the linkagegroup L¹¹ or L^(2k) in formula (1).

When the chromophores forming dye residues represented by Dye¹¹, Dye¹²and Dye^(2k) are merocyanine dyes, the merocyanine dyes are preferablythose represented by the following formula (4):

In the above formula, Za³ represents atoms forming a 5- or 6-memberednitrogen-containing heterocyclic ring which may further be fusedtogether with a benzene ring, a benzofuran ring, a pyridine ring, apyrrole ring, an indole ring or a thiophene ring. Za⁴ represents atomsforming an acidic nucleus. Ra³ represents any of a hydrogen atom, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedalkenyl group, a substituted or unsubstituted aryl group and asubstituted or unsubstituted heterocyclic group (suitable examples ofthese groups include the same groups as recited for Ra¹ and Ra²). Ma⁸ toMa¹¹ each represent a methine group independently (suitable examples ofthis group include the same groups as recited for Ma¹ to Ma⁷). na³ is 0or 1. ka² represents an integer of 0 to 3, preferably an integer of 0 to2. Q represents an ion neutralizing electric charge, and y is a numberrequired for neutralization of electric charge.

When ka² is 2 or 3, Ma¹⁰s and Ma¹¹s may be the same or different.Incidentally, the dye residue formed by removing a hydrogen atom fromany of Za³, Za⁴, Ra³ and Ma⁸ to Ma¹¹ in formula (4) can be chosen as adye residue in formula (1) and enter into combination with the linkagegroup L¹¹ or L^(2k) in formula (1).

When the chromophores forming dye residues represented by Dye¹¹, Dye¹²and Dye^(2k) are oxonol dyes, the oxonol dyes are preferably thoserepresented by the following formula (5):

In the above formula, Za⁵ and Za⁶ each represent atoms forming an acidicnucleus independently. Ma¹² to Ma¹⁴ each represent a substituted orunsubstituted methine group independently (suitable examples of thisgroup include the same groups as recited for Ma¹ to Ma⁷). ka³ representsan integer of 0 to 3, preferably an integer of 0 to 2, far preferably 1or 2. When ka³ is 2 or 3, Ma¹²s and Ma¹³s may be the same or different.

Q represents an ion neutralizing electric charge, and y is a numberrequired for neutralization of electric charge.

Incidentally, the dye residue formed by removing a hydrogen atom fromany of Za⁵, Za⁶ and Ma¹² to Ma¹⁴ in formula (5) can be chosen as a dyeresidue in formula (1) and enter into combination with the linkage groupL¹¹ or L^(2k) in formula (1).

Examples of groups which Za¹, Za² and Za³ constitute respectivelyinclude groups derived from 3-25C oxazole nuclei (e.g.,2-3-methyloxazolyl, 2-3-ethyloxazolyl, 2-3,4-diethyloxazolyl,2-3-methylbenzoxazolyl, 2-3-ethylbenzoxazolyl,2-3-sulfoethylbenzoxazolyl, 2-3-sulfopropylbenzoxazolyl,2-3-methylthioethylbenzoxazolyl, 2-3-methoxyethylbenzoxazolyl,2-3-sulfobutylbenzoxazolyl, 2-3-methyl-β-naphthoxazolyl,2-3-methyl-α-naphthoxazolyl, 2-3-sulfopropyl-β-naphthoxazolyl,2-3-sulfopropyl-α-naphthoxazolyl, 2-3-(3-naphthoxyethyl)benzoxazolyl,2-3,5-dimethylbenzoxazolyl, 2-6-chloro-3-methylbenzoxazolyl,2-5-bromo-3-methylbenzoxazolyl, 2-3-ethyl-5-methoxybenzoxazolyl,2-5-phenyl-3-sulfopropylbenzoxazolyl,2-5-(4-bromophenyl)-3-sulfobutylbenzoxazolyl,2-3-methyl-5,6-dimethylthiobenzoxazolyl), groups derived from 3-25Cthiazole nuclei (e.g., 2-3-methylthiazolyl, 2-3-ethylthiazolyl,2-3-sulfopropylthiazolyl, 2-3-sulfobutylthiazolyl,2-3,4-dimethylthiazolyl, 2-3,4,5-trimethylthiazolyl,2-3-carboxyethylthiazolyl, 2-3-methylbenzothiazolyl,2-3-ethylbenzothiazolyl, 2-3-butylbenzothiazolyl,2-3-sulfopropylbenzothiazolyl, 2-3-sulfobutylbenzothiazolyl,2-3-methyl-β-naphthothiazolyl, 2-3-sulfopropyl-γ-naphthothiazolyl,2-3-(1-naphthoxyethyl)benzothiazolyl, 2-3,5-dimethylbenzothiazolyl,2-6-chloro-3-methylbenzothiazolyl, 2-6-iodo-3-ethylbenzothiazolyl,2-5-bromo-3-methylbenzothiazolyl, 2-3-ethyl-5-methoxybenzothiazolyl,2-5-phenyl-3-sulfopropylbenzothiazolyl,2-5-(4-bromophenyl)-3-sulfobutylbenzothiazolyl,2-3-methyl-5,6-dimethylthiobenzothiazolyl), groups derived from 3-25Cimidazole nuclei (e.g., 2-1,3-diethylimidazolyl,2-1,3-dimethylimidazolyl, 2-1-methylbenzimidazolyl,2-1,3,4-triethylimidazolyl, 2-1,3-diethylbenzimidazolyl,2-1,3,5-trimethylimidazolyl, 2-6-chloro-1,3-dimethylbenzimidazolyl,2-5,6-dichloro-1,3-diethylbenzimidazolyl,2-1,3-disulfopropyl-5-cyano-6-chlorobenzimidazolyl), groups derived from10-30C indolenine nuclei (e.g., those derived from3,3-dimethylindolenine), groups derived from 9-25C quinoline nuclei(e.g., 2-1-methylquinolyl, 2-1-ethylquinolyl,2-1-methyl-6-chloroquinolyl, 2-1,3-diethylquinolyl,2-1-methyl-6-methylthioquinolyl, 2-1-sulfopropylquinolyl,4-1-methylquinolyl, 4-1-sulfoethylquinolyl, 4-1-methyl-7-chloroquinolyl,4-1,8-diethylquinolyl, 4-1-methyl-6-methylthioquinolyl,4-1-sulfopropylquinolyl), groups derived from 3-25C selenazole nuclei(e.g., 2-3-methylbenzoselenazolyl) and groups derived from pyridinenuclei (e.g., 2-pyridyl). Other examples of heterocyclic nuclei formedby Za¹, Za² and Za³ respectively include tiazoline nuclei, oxazolinenuclei, selenazoline nuclei, tetrazoline nuclei, tellurazole nuclei,benzotellurazole nuclei, imidazoline nuclei, imidazo[4,5-quinoxaline]nuclei, oxadiazole nuclei, thiadiazole nuclei, tetrazole nuclei andpyrimidine nuclei. These nuclei may have substituents. Suitable examplesof such substituents include alkyl groups (e.g., methyl, ethyl, propyl),halogenatoms (e.g., chlorine, bromine, iodine, fluorine, a nitro group,alkoxy groups (e.g., methoxy, ethoxy), aryl groups (e.g., phenyl),heterocyclic groups (e.g., 2-pyridyl, 3-pyridyl, 1-pyrrolyl, 2-thienyl),aryloxy groups (e.g., pehnoxy), acylamino groups (e.g., acetylamino,benzoylamino), carbamoyl groups (e.g., N,N-dimethylcarbamoyl), a sulfogroup, sulfonamido groups (e.g., methanesulfonamido), sulfamoyl groups(e.g., N-methylsulfamoyl), a hydroxyl group, a carboxyl group, alkylthiogroups (e.g., methylthio) and a cyano group. Of the nuclei recitedabove, the oxazole nuclei, the imidazole nuclei and the thiazole nucleiare preferred over the others. These nuclei may further be fusedtogether with other rings. Examples of rings to be fused include benzenerings, benzofuran rings, pyridine rings, pyrrole rings, indole rings andthiophene rings.

Za⁴, Za⁵ and Za⁶ each represent atoms required for forming an acidicnucleus as defined in The Theory of the Photographic Process, 4thedition edited by James, page 198, Macmillan Publishing Co., Inc.(1997). Examples of such an acidic nucleus include pyrazol-5-one,pyrazolidine-3,5-dione, imidazoline-5-one, hydantoin, 2- or4-thiohydantoin, 2-iminooxazolidine-4-one, 2-oxazoline-5-one,2-thiooxazoline-2,4-dione, isorhodanine, rhodanine, thiophene-3-one,thiophene-3-one-1,1-dioxide, indoline-2-one, indoline-3-one,2-oxoindazolium, 5,7-dioxo-6,7-dihydrothiazolo[3,2-a]pyrimidine,3,4-dihydroisoquinoline-4-one, 1,3-dioxane-4,6-dione (e.g., meldrum'sacid), barbituric acid, 2-thiobarbituric acid, coumarin-2,4-dione,indazoline-2-one, pyrido[1,2-a]pyrimidine-1,3-dione,pyrazolo[1,5-b]quinazolone, pyrazolopyridone,3-dicyanomethylidenyl-3-phenylpropionitrile and 5- or 6-membered carbonring (e.g., hexane-1,3-dione, pentane-1,3-dione, indane-1,3-dione). Ofthese nuclei, pyrazole-5-one, barbituric acid, 2-thiobarbituric acid and1,3-dioxane-4,6-dione are preferred over the others.

Examples of cyanine dyes, merocyanine dyes and oxonol dyes include thosedescribed in F. M. Harmer, Heterocyclic Compounds—Cyanine Dyes andRelated Compounds, Jhon & Wiley & Sons, New York, London (1964).

In formula (1), L¹¹ and L^(2k) each represent a divalent linkage groupindependently, and have no particular restriction except that each ofthe linkage groups forms no π-conjugated system between the chromophoreslinked thereto, with suitable examples including 0-100C, preferably1-20C, linkage groups made up of one or more groups selected from amongalkylene groups (those containing 1 to 20 carbon atoms, such asmethylene, ethylene, propylene, butylene and pentylene), arylene groups(those containing 6 to 26 carbon atoms, such as phenylene andnaphthylene), alkynylene groups (those containing 2 to 20 carbon atoms,such as ethynylene and propnylene), —CO—N(R¹⁰¹)—, —CO—O—,—SO₂—N—(R¹⁰²)—, —SO₂—O—, —N(R¹⁰³)—CO—N(R¹⁰⁴)—, SO₂—, —SO—, —S—, —O—,—CO—, —N(R¹⁰⁵)— and heterylene groups (those containing 1 to 26 carbonatoms, such as 6-chloro-1,3,5-triazyl-2,4-diyl and pyrimidine-2,4-diyl).Herein, R¹⁰¹, R¹⁰², R¹⁰³, R¹⁰⁴ and R¹⁰⁵ each independently represent anyof a hydrogen atom, a substituted or unsubstituted alkyl group and asubstituted or unsubstituted aryl group. In addition, when L¹¹ andL^(2k) are each a combination of two or more of the linkage groups asrecited above, at least two (preferably two) of the linkage groups maycombine with each other to form a ring.

As L¹¹ and L^(2k) each, the linkage group formed by bonding two alkylenegroups (preferably including ethylene) together to form a ring,especially a 5- or 6-membered ring (preferably a cyclohexane ring), ispreferred.

In formula (1), n is an integer of 0 to 10, preferably 0 to 5, farpreferably 0 to 3, particularly preferably 0 to 2.

In formula (1), k represents all integers in the 0 to n range. Forinstance, when n is 2, k represents three integers of 0, 1 and 2,Dye^(2k) represents three independent chromophores Dye²⁰, Dye²¹ andDye²², and L^(2k) represents three independent linkage groups L²⁰, L²¹and L²². When n is an integer greater than one, two or more chromophoresrepresented by Dye^(2k) may be the same or different, and two or morelinkage groups represented by L^(2k) may be the same or different.

In formula (1), Q represents an ion neutralizing electric charge, and yis a number required for neutralization of electric charge. Whether acertain compound is a cation or an anion, or whether it has net ioniccharge or not, depends on what kind of substituent the compound has. Informulae (1), (3), (4) and (5) each, the ion represented by Q has threecases depending on the electric charge of its counter dye molecule: acase where it is a cation, a case where it is an anion, and a case whereQ is absent when the dye molecule has no electric charge. The ionrepresented by Q has no particular restrictions, but it may be an ionderived from an inorganic compound or an ion derived from an organiccompound. In addition, the electric charge of an ion represented by Qmay be univalent or polyvalent. Examples of a cation represented by Qinclude metal ions such as sodium ion and potassium ion, and onium ionssuch as quaternary ammonium ions, oxonium ions, sulfonium ions,phosphonium ions, selenonium ions and iodonium ions. Examples of ananion represented by Q include halide anions such as chloride ion,bromide ion and fluoride ion, heteropolyacid ions such as sulfate ion,phosphate ion and hydrogen phosphate ion, organic polyvalent anions suchas succinate ion, maleate ion, fumarate ion and aromatic disulfonateions, tetrafluoroborate ion and hexafluorophosphate ion.

The ions suitable as cation represented by Q are onium ions, especiallyquaternary ammonium ions. Of the quaternary ammonium ions, the4,4′-bipyridinium cations represented by formula (1-4) inJP-A-2000-52658 and the 4,4′-bipyridinium cations disclosed inJP-A-2000-59652 are preferred in particular.

The ions suitable as anion represented by Q are tetrafluoroborate ion,hexafluorophosphate ion and organic polyvalent anions, especially 2- or3-valent organic anions derived from naphthalenedisulfonic acidderivatives. Of the 2- or 3-valent organic anions, thenaphthalenedisulfonic acid anions disclosed in JP-A-10-226170 arepreferred in particular.

Of the dyes represented by formula (1), dyes having structuresrepresented by the following formula (6) are preferred over the othersas the dye used in the present optical information-recording medium:

wherein Za²¹, Za²², Za²³ and Za²⁴ each represent atoms forming an acidicnucleus independently, and as concrete examples of Za²¹, Za²², Za²³ andZa²⁴, the acidic nuclei described for Za⁵ and Za⁶ in formula (5)described above are exemplified. Also, the preferred examples thereofare the same as in the above described Za⁵ and Za⁶.

Ma²¹, Ma²², Ma²³, Ma²⁴, Ma²⁵ and Ma²⁶ each represent a substituted orunsubstituted methine group independently, and as concrete examples ofMa²¹, Ma²², Ma²³, Ma²⁴, Ma²⁵ and Ma²⁶ the same meaning as described forMa¹ to Ma⁷ in formula (3) described above.

L¹¹ is a divalent linkage group forming no π-conjugated system togetherwith its two bonds, and as concrete examples of L¹¹, ones described forL¹¹ and L^(2k) in formula (1) described above are exemplified.

Ka²¹ and Ka²² each represent an integer of 0 to 3, preferably 0 to 2 andmore preferably 1 or 2, independently; and Ma²¹s, Ma²²s, Ma²⁵s and Ma²⁶spresent in a case where Ka²¹ and Ka²² are each 2 or 3 may be the same ordifferent.

Q represents a univalent cation for neutralizing electric charge, or 2Qrepresents a divalent cation, and as concrete examples and preferredexamples of Q, ones described in a case where Q in formula (1) is acation are exemplified, respectively.

It is most advantageous for the present optical information-recordingmedium to contain a dye having a structure represented by formula (2) asthe dye represented by formula (1).

In formula (2), R¹¹, R¹², R¹³ and R¹⁴ each independently represent anyof a hydrogen atom, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted aryl group and a substituted orunsubstituted heterocyclic group. Examples of substituted orunsubstituted alkyl groups represented by R¹¹, R¹², R¹³ and R¹⁴respectively include 1-20C alkyl groups (e.g., methyl, ethyl, propyl,butyl, i-butyl, t-butyl, i-amyl, cyclopropyl, cyclohexyl, benzyl,phenetyl). When R¹¹, R¹², R¹³ and R¹⁴ are each an alkyl group, carbonrings (e.g., cyclopropane, cyclobutane, cyclopentane, cyclohexane,2-methylcyclohexane, cycloheptane, cyclooctane) or heterocyclic rings(e.g., pyridine, chroman, morpholine) may be formed by combining R¹¹with R¹² and, at the same time, combining R¹³ with R¹⁴. The alkyl groupsuitable as R¹¹, R¹², R¹³ and R¹⁴ each is a 1-8C open-chain or cyclicalkyl group, especially a 1-5C open-chain (straight or branched) alkylgroup, an alkyl group capable of forming a 1-8C ring (preferably acyclohexane ring) as a combination of R¹¹ and R¹² or as a combination ofR¹³ and R¹⁴, or a 1-20C substituted alkyl group (e.g., benzyl,phenetyl).

Examples of a substituted or unsubstituted aryl group represented byR¹¹, R¹², R¹³ and R¹⁴ each in formula (2) include 6-20C aryl groups(e.g., phenyl, naphthyl). The aryl group suitable as R¹¹, R¹², R¹³ andR¹⁴ each is a 6-10C aryl group.

The substituted or unsubstituted heterocyclic group represented by R¹¹,R¹², R¹³ and R¹⁴ each in formula (2) is a 5- or 6-membered saturated orunsaturated heterocyclic group made up of carbon atoms and nitrogen,oxygen or/and sulfur atom(s), with examples including a pyridyl group, apyrimidyl group, a pyridazyl group, a piperidyl group, a triazyl group,a pyrrolyl group, an imidazolyl group, a triazolyl group, a furanylgroup, a thiophenyl group, a thiazolyl group, an oxazolyl group, anisothiazolyl group and an isoxazolyl group. Further, the heterocyclicgroup may be a group formed by fusing each of the above-recited groupstogether with a benzene ring (such as a quinolyl group, a benzimidazolylgroup, a benzothiazolyl group or a benzoxazolyl group). The substitutedor unsubstituted heterocyclic group suitable as R¹¹, R¹², R¹³ and R¹⁴each is a 6-10C substituted or unsubstituted heterocyclic group.

Examples of a substituent present in the substituted or unsubstitutedalkyl group, the substituted or unsubstituted aryl group and thesubstituted or unsubstituted heterocyclic group represented by each ofR¹¹, R¹², R¹³ and R¹⁴ in formula (2) include a group S of substituentsas recited below.

In the group S are included 1-20C alkyl groups (e.g., methyl, ethyl,propyl, carboxymethyl, ethoxycarbonylmethyl), 7-20C aralkyl groups(e.g., benzyl, phenetyl), 1-8C alkoxy groups (e.g., methoxy, ethoxy),6-20C aryl groups (e.g., phenyl, naphthyl), 6-20C aryloxy groups (e.g.,phenoxy, naphthoxy), heterocyclic groups (e.g., pyridyl, pyrimidyl,pyridazyl, benzimidazolyl, benzothiazolyl, benzoxazolyl,2-pyrrolidinone-1-yl, 2-piperidone-1-yl, 2,4-dioxyimidazolidine-3-yl,2,4-dioxyoxazolidine-3-yl, succinimido, phthalimido, maleimido), halogenatoms (e.g., fluorine, chlorine, bromine, iodine), a carboxyl group,2-10C alkoxycarbonyl groups (e.g., methoxycarbonyl, ethoxycarbonyl), acyano group, 2-10C acyl groups (e.g., acetyl, pivaloyl), 1-10C carbamoylgroups (e.g., carbamoyl, methylcarbamoyl, morpholinocarbamoyl), an aminogroup, 1-20C substituted amino group (e.g., dimethylamino, diethylamino,bis(methylsulfonylethyl)amino, N-ethyl-N′-sulfoethylamino), a sulfogroup, a hydroxyl group, a nitro group, 1-10C sulfonamido groups (e.g.,methanesulfonamido), 1-10C ureido groups (e.g., ureido, methylureido),1-10C sulfonyl groups (e.g., methanesulfonyl, ethanesulfonyl), 1-10Csulfinyl groups (e.g., methanesulfinyl), and 0-10C sulfamoyl groups(e.g., sulfamoyl, methanesulfamoyl). When the substituent is a carboxylgroup or a sulfo group, it may be in a salt state.

In formula (2), R²¹, R²² and R³ each independently represent any of ahydrogen atom, a substituted or unsubstituted alkyl group, a substitutedor unsubstituted alkoxy group, a substituted or unsubstituted arylgroup, a substituted or unsubstituted aryloxy group, a substituted orunsubstituted heterocyclic group, a halogen atom, a carboxyl group, asubstituted or unsubstituted alkoxycarbonyl group, a cyano group, asubstituted or unsubstituted acyl group, a substituted or unsubstitutedcarbamoyl group, an amino group, a substituted amino group, a sulfogroup, a hydroxyl group, a nitro group, a substituted or unsubstitutedalkylsulfonylamino group, a substituted or unsubstituted carbamoylaminogroup, a substituted or unsubstituted alkylsulfonyl group, a substitutedor unsubstituted arylsulfonyl group, a substituted or unsubstitutedsulfinyl group, and a substituted or unsubstituted sulfamoyl group. Itis appropriate that R²¹, R²² and R³ be each a hydrogen atom, asubstituted or unsubstituted 1-20C alkyl group, a substituted orunsubstituted 2-20C heterocyclic group, a substituted or substituted1-20C alkoxy group, a substituted or substituted 6-20C aryl group, or ahalogen atom. Further, any of a hydrogen atom, a substituted orunsubstituted 1-10C alkyl group, a subsituted or unsubstituted 1-10Calkoxy group, a substituted or unsubstituted 2-10C heterocyclic groupand a halogen atom, especially any of a hydrogen atom, a substituted orunsubstituted 1-5C alkyl group, a substituted or unsubstituted 1-5Calkoxy group, a substituted or unsubstituted 2-6C heterocyclic group anda halogen atom, is preferred as R²¹, R²² and R³ each. The groups thatR²¹, R²² and R³ represent may further have substituents, and examples ofsuch substituents include the group S mentioned above.

It is preferable that m is 0 and both R²¹ and R²² are hydrogen atoms, orm is 1 and all of R²¹, R²² and R³ are hydrogen atoms. m in formula (2)represents an integer of 0 or more, preferably an integer of 0 to 5, farpreferably an integer of 0 to 3, particularly preferably an integer of 0to 2.

When m is 2 and above, R³s in formula (2) may be the same or differentand each represent a hydrogen atom or the above-mentioned substituentindependently.

Z^(x+) in formula (2) represents a cation, and x represents an integerof 1 or greater.

Examples of a cation represented by Z^(x+) include the cations recitedas examples of Q in formula (1). The cations suitable as Z^(x+) arequaternary ammonium ions, preferably the 4,4′-bipyridinium cationsrepresented by formula (I-4) in JP-A-2000-52658 and the4,4′-bipyridinium cations disclosed in JP-A-2000-59652. x in formula (2)is preferably an integer of 1 or 2.

Dyes represented by the present formula (2) are novel compoundssynthesized by the present Inventors for the first time.

Examples of compounds represented by the present formula (1) or formulae(2) and (6) are illustrated below, but these examples should not beconstrued as limiting the scope of the invention.

The general oxonol dye part can be synthesized by condensation reactionbetween an appropriate active methylene compound and a methine source (acompound used for introducing a methine group into a methine dye). Fordetails of compounds of this kind, JP-A-39-22069, JP-A-43-3504,JP-B-52-38056, JP-B-54-38129, JP-B-55-10059, JP-B-58-35544,JP-A-49-99620, JP-A-52-92716, JP-A-59-16834, JP-A-63-316853,JP-A-64-40827, British Patent No. 1,133,986, and U.S. Pat. Nos.3,247,127, 4,042,397, 4,181,225, 5,213,956 and 5,260,179 can be referredto.

As the dyes represented by formulae (3) to (5), those disclosed inpatent documents, e.g., WO 02/080161A2, JP-A-63-209995 and JP-A-2-62279,can be utilized.

The present dye compounds represented by formula (2) can be synthesizedin accordance with the following reaction scheme:

Incidentally, a dye part having a higher number of chromophores than thedye part 3-II can be obtained by using the linkage part 2-I preparedunder the scheme (2) in place of Compound 1-I in the reaction betweenCompound 3-I and Compound 1-I.

The present dye compounds represented by formula (2) may be used aloneor as combinations of two or more thereof. In addition, these dyecompounds relating to the invention may be used in combination withother dye compounds.

The present information-recording medium is not particularly restrictedexcept that it has a recording layer containing a dye compoundrepresented by formula (2). When it is applied to CD-R, however, thepresent optical information-recording medium is preferred to have astructure that the recording layer containing a dye compound representedby formula (1), a light reflecting layer and a protective layer areprovided in order of mention on a 1.2±0.2 mm-thick transparentdisk-shape substrate wherein are formed a pregroove having a track pitchof 1.4 μm to 1.8 μm. On the other hand, when the present recordingmedium is applied to DVD-R, the following are two preferred embodimentsthereof:

(i) An optical information-recording medium made up of two laminates,which each have a recording layer containing a dye compound representedby formula (1) and a light reflecting layer on a 0.6±0.1 mm-thicktransparent disk-shape substrate having a pregroove formed with a trackpitch of 0.6 to 0.9 μm, bonded together with the recording layers insideso as to have a total thickness of 1.2±0.2 mm.

(ii) An optical information-recording formed by bonding a laminate madeup of a 0.6±0.1 mm-thick transparent disk-shape substrate having apregroove formed with a track pitch of 0.6 to 0.9 μm, a recording layercontaining a dye compound represented by formula (1) and a lightreflecting layer to a disk-shape protective plate having the samedimensions as the laminate with the recording layer inside so as to havea total thickness of 1.2±0.2 mm. Incidentally, the opticalinformation-recording media of DVD-R type can have structures thatprotective layers are further provided on the irrespective lightreflecting layers.

The present information-recording medium can be produced using, e.g.,the methods as described below. The substrate of the present medium(including the protective substrate also) can be arbitrarily selectedfrom various materials hitherto used for substrates ofinformation-recording media. Examples of a substrate material usableherein include glass, polycarbonate, acrylic resins such as polymethylmethacrylate, vinyl chloride resins such as polyvinyl chloride and vinylchloride copolymers, epoxy resin, amorphous polyolefin and polyester.These materials may be used in combination of two or more thereof, ifdesired. Incidentally, they may be used in the form of film or rigidplate. Of those materials, polycarbonate is preferred over the othersfrom the viewpoints of moisture resistance, dimensional stability andprice.

On the side of the substrate surface where the recording layer isprovided, a subbing layer may be coated for the purposes of improvementsin flatness and adhesiveness and prevention of deterioration. Examplesof a material for forming the subbing layer include macromolecularsubstances, such as polymethyl methacrylate, acrylic acid-methacrylicacid copolymer, styrene-maleic acid anhydride copolymer, polyvinylalcohol, N-methylolacrylamide, styrene-vinyltoluene copolymer,chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride,chlorinated polyolefin, polyester, polyimide, vinyl acetate-vinylchloride copolymer, ethylene-vinyl acetate copolymer, polyethylene,polypropylene and polycarbonate; and surface modifiers such as silanecoupling agents. In forming the subbing layer, a coating composition isprepared first by dissolving or dispersing a substance as recited abovein an appropriate solvent, and then applied to a substrate surface inaccordance with a coating method such as spin coating, dip coating orextrusion coating.

Further, a tracking groove or asperity representing information such asaddress signals (pregroove) is formed on the substrate (or the subbinglayer). It is preferable that the pregroove is formed directly on thesubstrate with the foregoing track pitch at the time of injection orextrusion molding of a resin material such as polycarbonate.Alternatively, the pregroove may be formed by providing a pregroovelayer. As a material for the pregroove layer, a mixture of at least onemonomer (or oligomer) chosen from monoesters, diesters, triesters ortetraesters of acrylic acid with a photo-polymerization initiator can beused. The pregroove layer can be formed, e.g., in the following manner:Firstly a solution of the foregoing mixture of an acrylic acid ester anda photo-polymerization initiator is coated on a precisely formed matrix(stamper), and then a substrate is mounted on the coating solution layerand irradiated with ultraviolet rays via the substrate or the stamper,thereby curing the coating layer and fixing the substrate to the coatinglayer. Thereafter, the substrate is peeled from the stamper.

On the pregroove-formed surface of the substrate (or the subbing layer),a recording layer containing the dye as defined in (1), preferably thepresent dye compound represented by formula (1), is provided.

The recording layer can further contain various types of discolorationinhibitors for the purpose of obtaining an improvement in lightresistance. The representatives of discoloration inhibitors usabletherein include the metal complexes, the diimmonium salts and theaminium salts represented by formulae (III), (IV) and (V) respectivelyin JP-A-3-224793, the nitroso compounds disclosed in JP-A-2-300288, andthe TCNQ derivatives disclosed in JP-A-10-151861.

The recording layer can be formed by dissolving the present dye and, ifneeded, a quencher and a binder in a solvent to prepare a coatingsolution, coating the coating solution on a substrate surface to form acoating layer, and then drying the coating layer. Examples of a solventof the coating solution used for forming the dye recording layer includeesters, such as butyl acetate, ethyl lactate and cellosolve acetate;ketones, such as methyl ethyl ketone, cyclohexanone and methyl isobutylketone; chlorinated hydrocarbons, such as dichloromethane,1,2-dichloroethane and chloroform; amides, such as dimethylformamide;hydrocarbons, such as cyclohexane; ethers, such as tetrahydrofuran,ethyl ether and dioxane; alcohol compounds, such as ethanol, n-propanol,isopropanol, n-butanol and diacetone alcohol; fluorine-containingsolvents, such as 2,2,3,3-tetrafluoropropanol; and glycol ethers, suchas ethylene glycol monomethyl ether, ethylene glycol monoethyl ether andpropylene glycol monomethyl ether. These solvents can be used alone oras combinations of two or more thereof with consideration for solubilityof compounds to be dissolved therein. To the coating solution, variousadditives including an antioxidant, a UV absorber, a plasticizer and alubricant may further be added according to the desired purposes.

Examples of a binder usable in the recording layer include naturallyoccurring organic macromolecular substances, such as gelatin, cellulosederivatives, dextran, rosin and rubber; and synthetic organic polymers,such as hydrocarbon resins (e.g., polyethylene, polypropylene,polystyrene, polyisobutylene), vinyl resins (e.g., polyvinyl chloride,polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer),acrylic resins (e.g., polymethyl acrylate, polymethyl methacrylate),polyvinyl alcohol, chlorinated polyethylene, epoxy resin, butyral resin,rubber derivatives, and initial condensation products of thermosettingresins such as phenol-formaldehyde resin. When such a binder is used asa constituent material of the recording layer in combination with thepresent dye, the amount of the binder used is generally from 0.01 to 50times (by weight), preferably from 0.1 to 5 times (by weight), that ofthe dye used. The dye concentration in the thus prepared coatingsolution is generally from 0.01 to 10 weight %, preferably from 0.1 to 5weight %.

Examples of a coating method applicable herein include a spray method, aspin coating method, a dip method, a roll coating method, a bladecoating method, a doctor roll method and a screen printing method. Therecording layer may be a single layer or a double layer. The thicknessof the recording layer is generally from 20 to 500 nm, preferably from50 to 300 nm.

On the recording layer, a reflective layer is provided for the purposeof improving the reflectivity at the time of information reproduction.The light-reflecting substance as a constituent material of thereflective layer is a substance having a high laser-light reflectivity,with examples including metals or semimetals, such as Mg, Se, Y, Ti, Zr,Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Ru, Rh, Pd, Ir, Pt, Cu,Ag, Au, Zn, Cd, Al, Ga, In, Si, Ge, Te, Pb, Po, Sn and Bi; and stainlesssteel. Of these substances, Cr, Ni, Pt, Cu, Ag, Au, Al and stainlesssteel are preferred over the others, and Ag in particular isadvantageous. These substances may be used alone, or as combinations oralloys of two or more thereof. The reflective layer can be formed on therecording layer by vapor deposition, sputtering or ion-plating of areflective substance as recited above. The thickness of the reflectivelayer is generally from 10 to 300 nm, preferably from 50 to 200 nm.

On the reflective layer, a protective layer may be provided for thepurpose of protecting the recording layer from physical and chemicaldamages. For the purpose of enhancing scratch resistance and moistureresistance, such a protective layer may also be provided on the side ofthe substrate where the recording layer is not provided. Examples of asubstance usable for the protective layer include inorganic substances,such as SiO, SiO₂, MgF₂, SnO₂ and Si₃N₄; and organic substances, such asthermoplastic resins, thermosetting resins and UV-curable resins. Theprotective layer can be formed by laminating a substance as recitedabove on the reflective layer and/or the substrate via an adhesive layersuch as a film obtained by extrusion of plastic. Alternatively, theprotective layer may be formed using a vacuum deposition, sputtering orcoating method. In the case of using a thermoplastic resin or athermosetting resin, the protective layer can be formed by dissolvingthe resin in an appropriate solvent to prepare a coating solution,coating the coating solution and then drying the solution coated. In thecase of a UV-curable resin, the protective layer is formed by coatingthe resin as it is or a solution prepared by dissolving the resin in anappropriate solvent, and then irradiating the coating with UV rays tocure the resin. To those coating solutions, various additives, such asan antistatic agent, an antioxidant and a UV absorber, may further beadded according to the desired purposes. The thickness of the protectivelayer is generally from 0.1 to 100 μm. Through the process mentionedabove, a laminate having on the substrate the recording layer, thereflective layer and, if needed, the protective layer can be formed. Anda DVD-R information-recording medium having two recording layers can beproduced by forming two laminates through the foregoing process andbonding them together with their respective recording layers inside. Inaddition, a DVD-R information-recording medium having the recordinglayer on one side alone can be produced by bonding one laminate formedthrough the above process to a disk-shape protective substrate havingthe same dimensions as the substrate of the laminate with the recordinglayer inside.

In the invention, recording of information on the thus producedinformation-recording media is performed, e.g., in the following manner.While rotating an information-recording medium at a constant linearvelocity or a constant angular velocity, laser light for recording, suchas semiconductor laser light, is applied to the information-recordingmedium from the substrate side. By this exposure to laser light, it isthought that cavities are formed at the interface between the recordinglayer and the reflective layer (the cavity formation occurs as therecording layer or the reflective layer, or both of them undergodeformation), or swelling deformations are caused in the substrate, ordiscoloration or change of association state is caused in the recordinglayer, and thereby changes in refractive index are achieved to result inrecording of information. As the recording light, semiconductor laserbeams having oscillation wavelengths in the range of 770 to 790 nm areused in the case of CD-R type of recording media, and those havingoscillation wavelengths in the range of 600 to 700 nm (preferably 620 to680 nm, far preferably 630 to 660 nm) are used in the case of DVD-R typeof recording media. The information thus recorded can be reproduced byirradiating the substrate side of the information-recording medium withsemiconductor laser light having the same wavelength as the light usedat the time of recording while rotating the recording medium at the sameconstant linear velocity as set for the recording, and detecting thelight reflected from the recording medium.

EXAMPLES Example 1

Synthesis of Compound (3):

The present compound was synthesized in accordance with the reactionscheme illustrated hereinbefore.

[Synthesis of Linkage Part (Compound (1-I))]

1,4-Cyclohexanedione (22.43 g, 0.2 mol) and malonic acid (41.62 g, 0.4mol) were dissolved in acetic anhydride (85 ml), and theretoconcentrated sulfuric acid (7.0 ml, 0.12 mol) was added. The resultingadmixture was stirred in an ice bath. As the reaction progressed, lightbrown crystals separated out. These crystals were filtered off, washedwith ice-cold distilled water, and dried. Thus, 8.8 g of the intendedCompound (1-I) was obtained as light brown crystals (in a 15.5% yield.

[Synthesis of Dye Part (Compound (3-II))]

Malonic acid (5.2 g, 0.05 mol) and concentrated sulfuric acid (0.5 ml)were added to acetic anhydride (10 ml), and therein the source compoundwas dissolved thoroughly while stirring at room temperature. Thereto,4-ethylcyclohexanone (6.31 g, 0.05 mol) was slowly added dropwise whilecooling in an ice bath. The stirring of the admixture was continued inan ice bath, and colorless crystals separated out as the reactionprogressed. These crystals were filtered off, washed with distilledwater, and dried. Thus, 9.0 g of a meldrum's acid derivative wasobtained as colorless crystals (in a 85.1% yield). The thus obtainedmeldrum's acid derivative (4.25 g, 0.02 mol) andN,N′-1,3-pentadiene-1-yl-5-ylidenedianiline hydrochloride (5.70 g, 0.02mol) were dissolved in methanol (50 ml), and thereto triethylamine (3.04g, 0.03 mol) was added. The stirring of the resulting admixture wascontinued at room temperature to result in deposition of violetcrystals. Then, these crystals were filtered off, and washed withmethanol. Thus, 5.61 g of violet crystals corresponding to Compound(3-I) was obtained (in a 76.3% yield). These violet crystals (4.40 g,12.0 mmol) and the Compound (1-I) obtained in the foregoing Synthesis(1.71 g, 6.0 mmol) were dissolved in dimethylformamide (20 ml), andthereto triethylamine (1.82 g, 18 mmol) was added dropwise. Theresulting admixture was stirred for 4 hours at 50° C. Thereafter, thereaction solution obtained was admixed with distilled water, andextracted with ethyl acetate. The organic layer thus extracted waspurified by column chromatography (dichloromethane/methanol=6/1) onsilica gel to give 2.0 g of violet powder corresponding to Compound(3-II) (in a 39.5% yield).

[Synthesis of Dye Compound]

The violet powder (1.24 g, 1.48 mmol) obtained in the foregoingSynthesis was dissolved into dimethylformamide in a minimum amountrequired for dissolution, and thereto Compound C used as a countercation was added at room temperature with stirring. The stirring wascontinued to result in deposition of gold powder. So the gold powder wasfiltered off, thereby giving 0.95 g of the desired Compound (3) as gold(in a 48.3% yield).

The molecular structure of the thus obtained gold powder was confirmedby ¹H-NMR.

¹H-NMR (DMSO-d₆): 0.84(t, 6H), 1.20(m. 10H), 1.62(m. 8H), 1.96-2.14(m,12H), 7.11(m. 4H), 7.24(d, 2H), 7.34-7.77(m, 18H), 7.90(d, 2H), 9.00(d,4H), 9.65(d, 4H), 10.71(s, 2H)

Example 2

Syntheses of Compounds (1), (13) and (14):

Synthesis was carried out under the same reaction scheme as thesynthesis of Compound (3) in Example 1, except for the scheme (3)wherein cyclohexanone was used in place of 4-ethylcyclohexanone; as aresult, the purification by column chromatography on silica gel in thescheme (3) effected resolution into the compound corresponding to thedye anion of Compound (1) and the compound corresponding to the dyeanion common to Compounds (13) and (14). And in the scheme (4), the thusresolved compounds corresponding to the dye anions were converted intotheir respective salts, thereby giving the desired Compound (1),Compound (13) and Compound (14).

¹H-NMR (DMSO-d₆) of Compound (1): 1.40(s, 4H), 1.54(s, 8H), 1.83 (s,8H), 1.98(s, 8H), 7.09-7.79(m, 24H), 7.92(s, 2H), 9.00(s, 4H), 9.69(s,4H)

¹H-NMR (DMSO-d₆) of Compounds (13): 1.41(s, 4H), 1.53(s, 8H), 1.82(s,8H), 1.98 (s, 24H), 7.13(t, 8H), 7.27(d, 4H), 7.38-7.79(m, 40H), 7.91(s,4H), 9.01(d, 8H), 9.67(d, 8H), 10.74(s, 4H)

Example 3

Synthesis of Compound (2):

Compound (2) was synthesized under the same reaction scheme as Compound(3) in Example 1, except that 4-methylcyclohexanone was used in place of4-ethylcyclohexanone.

¹H-NMR (DMSO-d₆): 0.91(d, 6H), 1.20(q, 4H), 1.47(s, 2H), 1.65(m, 8H),2.01(m, 12H), 7.10(q, 4H), 7.28(d, 2H), 7.39-7.86(m, 18H), 7.89(s, 2H),9.01(d, 4H), 9.67(d, 4H), 10.71(s, 2H)

Example 4

Synthesis of Compound (4):

Compound (4) was synthesized under the same reaction scheme as Compound(3) in Example 1, except that menthone was used in place of4-ethylcyclohexanone.

¹H-NMR (DMSO-d₆): 0.81(t, 12H), 0.90(d, 8H), 1.21(t, 2H), 1.41(s, 4H),1.61(t, 4H), 1.72(d, 2H), 1.97(s, 8H), 2.18(d, 4H), 7.12(q, 4H), 7.24(d,2H), 7.38-7.78(m, 18H), 7.90(s, 2H), 9.01(d, 4H), 9.68(d, 4H)_(,)10.71(s, 2H)

Example 5

Synthesis of Compound (5):

Compound (5) was synthesized under the same reaction scheme as Compound(3) in Example 1, except that 3,3,5-trimethylcyclohexanone was used inplace of 4-ethylcyclohexanone.

¹H-NMR (DMSO-d₆): 0.89(t, 12H), 0.97(s, 6H), 1.19(t, 2H), 1.40(m, 4H),1.89-1.98(m, 16H), 7.11(m, 4H), 7.26(d, 2H), 7.40(d, 2H), 7.49(m, 6H),7.60(t, 4H), 7.70(m, 6H), 7.90(s, 2H), 9.00(s, 4H), 9.67(s, 4H),10.72(s, 2H)

Example 6

Synthesis of Compound (6):

Compound (6) was synthesized under the same reaction scheme as Compound(3) in Example 1, except that methyl ethyl ketone was used in place of4-ethylcyclohexanone.

¹H-NMR (DMSO-d₆): 0.95(t, 6H), 1.53(s, 6H), 1.81(t, 4H), 1.99(s, 8H),7.11(q, 4H), 7.26(d, 2H), 7.39-7.77(m, 18H), 7.89(s, 2H), 9.00(d, 4H),9.67(d, 4H), 10.69(s, 2H)

Example 7

Synthesis of Compound (7):

Compound (7) was synthesized under the same reaction scheme as Compound(3) in Example 1, except that 3,3-dimethyl-2-butanone was used in placeof 4-ethylcyclohexanone.

¹H-NMR (DMSO-d₆): 1.10(s, 18H), 1.51(s, 6H), 1.98(s, 8H), 7.14(q, 4H),7.28(d, 2H), 7.38-7.78(m, 18H), 7.90(s, 2H), 9.01(d, 4H), 9.79(d, 4H),10.71(s, 2H)

Example 8

Synthesis of Compound (8):

Compound (8) was synthesized under the same reaction scheme as Compound(3) in Example 1, except that 2-methyl-3-pentanone was used in place of4-ethylcyclohexanone.

¹H-NMR (DMSO-d₆): 0.90(m, 18H), 1.83(q, 4H), 2.00(s, 8H), 2.15(m, 2H),7.11(q, 4H), 7.26(d, 2H), 7.38-7.75(m, 18H), 7.90(s, 2H), 9.01(d, 4H),9.68(d, 4H), 10.70(s, 2H)

Example 9

Synthesis of Compound (9):

Compound (9) was synthesized under the same reaction scheme as Compound(3) in Example 1, except that diethyl ketone was used in place of4-ethylcyclohexanone.

¹H-NMR (DMSO-d₆): 0.85(t, 12H), 1.84(q, 8H), 2.00(s, 8H), 7.11(q, 4H),7.26(d, 2H), 7.32-7.78(m, 18H), 7.89(s, 2H), 9.00(d, 4H), 9.66(d, 2H),10.701(s, 2H)

Example 10

Synthesis of Compound (10):

Compound (10) was synthesized under the same reaction scheme as Compound(3) in Example 1, except that 2-pentanone was used in place of4-ethylcyclohexanone.

¹H-NMR (DMSO-d₆): 0.90 (t, 6H), 1.39 (m, 4H), 1.45 (s, 6H), 1.77 (m,4H), 1.98(s, 8H), 7.10(q, 4H), 7.27(d, 2H), 7.40-7.80(m, 18H), 7.91(s,2H), 9.05(d, 4H), 9.65(d, 4H), 10.72(s, 2H)

Example 11

Synthesis of Compound (11):

Compound (11) was synthesized under the same reaction scheme as Compound(3) in Example 1, except that 3-methylcyclohexanone was used in place of4-ethylcyclohexanone.

¹H-NMR (DMSO-d₆): 0.98(m, 8H), 1.28(t, 2H), 1.50-1.65(m, 10H),1.96-2.08(m, 12H), 7.11(m, 4H), 7.25(d, 2H), 7.38-7.73(m, 18H), 7.90(s,2H), 9.00(s, 4H), 9.66(s, 4H), 10.70(s, 2H)

Example 12

Synthesis of Compound (12):

Compound (12) was synthesized under the same reaction scheme as Compound(3) in Example 1, except that cyclohexanone was used in place of4-ethylcyclohexanone and3-methyl-N,N′-1,5-heptadiene-1-yl-7-ylidenedianiline hydrochloride wasused in place of N,N′-1,3-pentadiene-1-yl-5-ylidenedianilinehydrochloride.

¹H-NMR (DMSO-d₆): 1.41 (s, 4H), 1.58(s, 8H), 1.82 (s, 8H), 1.99(s, 8H),1.99(s, 8H), 2.17(s, 6H), 7.24-7.48(m, 12H), 7.69-7.99(m, 12H), 9.00(s,4H), 9.68(s, 4H), 10.71(s, 2H)

Example 13

Evaluation of Optical Constant:

Optical characteristic values of the present dye compounds each (thereal part n and the imaginary part k of a complex refractive index) wereevaluated by reflex spectroscopic ellipsometry. As each sample formaking evaluations of optical characteristics by use of thespectroscopic ellipsometry, a spin coating film formed on a glasssubstrate was adopted. This spin coating film was formed by dissolvingeach dye compound into 2,2,3,3-tetrafluoropropanol so that the solutionconcentration reached 25 mM and casting this solution on a spinningglass substrate.

[Formation of Spin Coaing Film containing Comparative Compound (1)]

As a comparative example, a spin coating film was formed from acomparative compound (1) having the following structure and ensuringsatisfactory recording characteristics in the recording at equivalentspeed.

Optical characteristics of the spin coating films formed from thepresent Compounds (1) and (3) to (14) respectively were evaluated, and nand k values at 660 nm were determined from the evaluation resultsobtained. These values are shown in Table 1. TABLE 1 Compound n kCompound (1) 2.24 0.055 Compound (3) 2.23 0.054 Compound (4) 2.20 0.040Compound (5) 2.20 0.038 Compound (6) 2.27 0.040 Compound (7) 2.22 0.041Compound (8) 2.24 0.040 Compound (9) 2.25 0.047 Compound (10) 2.26 0.051Compound (11) 2.21 0.035 Compound (12) 2.21 0.051 Compound (13) 2.400.056 Compound (14) 2.30 0.050 Comparative Compound (1) 2.08 0.051

In the next place, examples of an optical information-recording mediumare shown.

Example 14

[Preparation of Optical Recording Medium]

By extrusion molding, polycarbonate resin was formed into a 0.6mm-thick, 120 mm-dia substrate having a spiral groove (depth: 130 nm,width: 310 nm, track pitch: 0.74 μm).

The present Compound (6) in an amount of 1.25 g was dissolved into 100ml of 2,2,3,3-tetrafluoropropanol to prepare a coating solution. Thiscoating solution was coated on the pregroove-formed surface of thesubstrate by use of a spin coating method, thereby forming a dye layer.

Onto the dye-coated surface, silver was sputtered to form a reflectivelayer having a thickness of about 150 nm. And the reflective layer thusformed was bonded to a 0.6 mm-thick dummy substrate by use of aUV-curable resin (Daicureclear SD640, produced by DAINIPPON INK ANDCHEMICALS, INCORPORATED), thereby forming a disc.

Comparative Example 1

A disc was formed in the same manner as in Example 14, except that theComparative Compound (1) illustrated above was used in place of thepresent Compound (6).

Comparative Example 2

A disc was formed in the same manner as in Example 14, except that a 6:4mixture of the Comparative Compound (1) and the following ComparativeCompound (2) was used in place of the present Compound (6).

[Evaluations of Optical Recording Medium]

By use of DDU-1000 and a multisignal generator (made by PulstecIndustrial Co., Ltd.; laser wavelength: 660 nm, aperture rate: 0.60),8-16 modulating signals were recorded at each of equivalent-speed (11.08Mbps), octuple-speed (88.64 Mbps) and decuple-speed (110.8 Mbps)transfer rates.

The recording strategies used are shown in Table 2 and FIG. 1. Theequivalent-speed recording and the decuple-speed recording were eachperformed using one kind of recording strategy, while the octuple-speedrecording was performed using two kinds of recording strategies greatlydifferent in pulse width.

The recording power was set so as to minimize the amount of jitter inrecording on each medium. Thereafter, the signals recorded werereproduced with laser of the same wavelength as that used for recording,and therein the amount of jitter was measured. The results obtained areshown in Table 3.

The optical recording media prepared in Example 14 had low jitter in allthe equivalent-speed, octuple-speed and decuple-speed reproductions aswell as high reflectivities, compared with those prepared in ComparativeExamples. With respect to the 8× recording characteristics, the mediumprepared in Example 14 achieved satisfactory jitter under each of therecording strategies greatly different in pulse width, compared with themedia prepared in Comparative Examples.

Further, when the single-frequency of 3T and 14T is recordedcorresponding to duodetuple-speed and hexadetuple-speed, the C/N ratio,modulation and jitter which are equivalent to those of equivalent-speedto decuple-speed were obtained. This fact means that the preferablecharacteristics are obtained in a case of the recording speed of atleast decuple-speed to hexadetuple-speed or hexadetuple-speed or more.TABLE 2 Recording Strategies Recording Speed 1× 8× 8× 10× RecordingStrategy A B C D 3Ttop 1.55 2.55 1.85 2.75 4Ttop 1.50 2.92 2.12 3.20nTtop 1.55 1.70 1.30 1.90 Tmp 0.65 — — — nTwt — 0.50 −0.30 0.55 nTlp —1.40 0.60 1.40 3-nTld — −0.03 −0.05 −0.03 3Tdtop — −0.15 −0.05 −0.154Tdtop — 0.20 0.35 0.20 nTdtop — 0.00 0.00 0.00 5Ttop2 — −0.15 −0.05−0.20 5Tlp2 — −0.10 −0.15 −0.20 5Tdlp2 — 0.00 0.00 0.00 P0/Pm — 1.481.58 1.36

TABLE 3 Evaluation Results of Recording Characteristics Example 14Comparative Example 1 Comparative Example 2 Recording speed 1× 8× 8× 10×1× 8× 8× 10× 1× 8× 8× 10× Recording strategy A B C D A B c D A B c DOptimum 11 28.5 36.3 33.5 12 29.0 39.0 34.0 7.9 25.5 29.5 29.2 recordingpower (mW) Reflectivity 53.2 51.8 52.0 50.9 50 49.1 49.0 48.6 44.5 46.544.8 44.4 (%) Jitter (%) 6.1 6.2 6.0 7.2 9.0 13.2 12.0 15.0 8 13.9 6.89.0 14T modulation 0.54 0.71 0.77 0.76 0.50 0.72 0.76 0.77 0.50 0.730.78 0.77 factor PI error 80 18 11 15 94 40 impossible impossible 94impossible 90 120 to measure to measure to measure AR (%) 50 32 28 25 4830 32 25 48 28 28 26

Example 15

Optical discs (Sample Nos. 202 to 213) were prepared in the same manneras the optical disc prepared in Example 14 (Sample No. 201), except thatthe dye Compound (6) was replaced by the present dye Compounds (7), (8),(9), (10), (15), (16), (17), (19), (21) and (22), Comparative Compound(1) and mixture of Comparative Compounds (1) and (2), respectively, asset forth in Table 4. And record-playback performances were evaluated bythe same method as in Example 14. The evaluation results thus obtainedare shown in Table 4. It can be seen from Table 4 that the present dyesensured higher reflectivity and lower jitter than the comparativecompounds as well as satisfactory modulation factor. TABLE 4 Reflec- 14ISample tivity Modulation No. Dye (%) Jitter Factor note 201 Compound (6)50.9 7.2 0.76 invention (Example 14) 202 Compound (7) 52.0 8.2 0.78invention 203 Compound (8) 51.2 8.1 0.77 invention 204 Compound (9) 52.27.9 0.77 invention 205 Compound (10) 52.4 8.1 0.78 invention 206Compound (15) 53.1 7.8 0.77 invention 207 Compound (16) 52.1 7.9 0.76invention 208 Compound (17) 53.9 8.4 0.75 invention 209 Compound (19)52.8 7.6 0.76 invention 210 Compound (21) 52.1 6.8 0.78 invention 211Compound (22) 51.6 8.1 0.78 invention 212 Comparative 48.6 15.0 0.77comparison Compound (1) 213 Mixture of 44.4 9.0 0.77 comparisonComparative Compounds (1) and (2)

The invention can provide dyes having complex refractive indexes greatin the real part n and equivalent or small in the imaginary part k,compared with those of comparative dyes for low-speed recording use, andcan offer an optical information-recording medium excellent recordingcharacteristics whether the recording speed is low or high. The entiredisclosure of each and every foreign patent application from which thebenefit of foreign priority has been claimed in the present applicationis incorporated herein by reference, as if fully set forth.

1-17. (canceled)
 18. An optical information-recording medium, comprisinga dye having at least two chromophores bonded to each other without anyconjugated bond intervening between said chromophores, wherein the dyeis represented by the following formula (1):

wherein Dye¹¹, Dye¹² and Dye^(2k) each independently represents a dyeresidue having a chromophore, L¹¹ and L^(2K) each independentlyrepresent a divalent linkage group forming no π-conjugated systembetween chromophores linked thereby, n represents an integer of 0 to 10,k represents all integers in the 0 to n range, Q represents an ionneutralizing electric charge, and y is a number required forneutralization of electric charge, and wherein the chromophores formingdye residues represented by Dye¹¹, Dye¹² and Dye^(2K) are cyanine dyesrepresented by the following formula (3) or merocyanine dyes representedby the following formula (4):

wherein Za¹ and Za² each represent atoms forming a 5- or 6-memberednitrogen-containing heterocyclic ring which may further be fusedtogether with a benzene ring, a benzofuran ring, a pyridine ring, apyrrole ring, an indole ring or a thiophene ring; Ra¹ and Ra² eachrepresent any of a hydrogen atom, a substituted or unsubstituted alkylgroup, a substituted or unsubstituted alkenyl group, a substituted orunsubstituted aryl group and a substituted or unsubstituted heterocyclicgroup; Ma¹ to Ma⁷ each independently represent a methine group which mayhave a substituent; na¹ and na² each represent 0 or 1 independently; ka¹represents an integer of 0 to 3, and when Ka¹ is 2 or 3, Ma³s and Ma⁴smaybe the same or different; Q represents an ion neutralizing electriccharge; and y is a number required for neutralization of electriccharge; the dye residue formed by removing a hydrogen atom from any ofZa¹, Za², Ra¹, Ra² and Ma¹ to Ma⁷ in formula (3) is chosen as a dyeresidue in formula (1) and enter into combination with the linkage groupL¹¹ or L^(2K) in formula (1), and

wherein Za³ represents atoms forming a 5- or 6-memberednitrogen-containing heterocyclic ring which may further be fusedtogether with a benzene ring, a benzofuran ring, a pyridine ring, apyrrole ring, an indole ring or a thiophene ring; Za⁴ represents atomsforming an acidic nucleus; Ra³ represents any of a hydrogen atom, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedalkenyl group, a substituted or unsubstituted aryl group and asubstituted or unsubstituted heterocyclic group; Ma⁸ to Ma¹¹ eachrepresent a methine group independently; na³ is 0 or 1; ka² representsan integer of 0 to 3, and when ka² is 2 or 3, Ma¹⁰s and Ma¹¹s maybe thesame or different; Q represents an ion neutralizing electric charge; andy is a number required for neutralization of electric charge; the dyeresidue formed by removing a hydrogen atom from any of Za³, Za⁴, Ra³ andMa⁸ to Ma¹¹ in formula (4) is chosen as a dye residue in formula (1) andenter into combination with the linkage group L¹¹ or L^(2k) in formula(1).
 19. An optical information-recording medium, comprising a dyehaving at least two chromophores bonded to each other without anyconjugated bond intervening between said chromophores, wherein the dyeis represented by the following formula (1):

wherein Dye¹¹, Dye¹² and Dye^(2K) each independently represents a dyeresidue having a chromophore L¹¹ and L^(2k) each independently representa divalent linkage group forming no π-conjugated system betweenchromophores linked thereby, n represents an integer of 0 to 2, krepresents all integers in the 0 to n range, Q represents an ionneutralizing electric charge, and y is a number required forneutralization of electric charge.
 20. An optical information-recordingmedium, comprising a dye having at least two chromophores bonded to eachother without any conjugated bond intervening between said chromophores,with the proviso that the dye is not a polymer.
 21. An opticalinformation-recording medium to be irradiated with laser light having awavelength of 600 to 700 nm, the medium comprising a dye having at leasttwo chromophores bonded to each other without any conjugated bondintervening between said chromophores, wherein the opticalinformation-recording medium has a thickness of 1.2±0.2 mm and comprisestwo laminates each containing a recording layer including the dye, inwhich the two laminates are bonded to each other so that each of therecording layers is inside, wherein each of the laminates includes: atransparent disk-shape substrate having a pregroove formed with a trackpitch of 0.6 to 0.9 μm and measuring one of 120±3 mm and 80±3 mm indiameter and 0.6±0.1 mm n thickness; and the recording layer provided onthe pregroove-formed side of the transparent disk-shape substrate.